Attention deficit disorder (ADD) remains one of the major clinical and public health problems in the U.S. in terms of morbidity and disability of children, adolescents and adults. Its impact on society is enormous in terms of financial cost, the stress to families, the impact on schools, the potentially damaging effects on self-esteem, and its potential for development of criminality and substance abuse. This proposal is aimed at evaluating familial and psychosocial risk factors of Attention Deficit Disorder (ADD). This application consists of two phases: 1. a "blind" initial assessment (case- control family study) and 2. a prospective longitudinal follow up study of these children and their siblings by subsequent annual follow-up evaluations of all children concentrating on psychopathology and psychosocial functioning. All probands and their first-degree relatives will be studied with an extensive battery of structured clinical interviews. All subjects will receive criterion-based lifetime and current diagnosis and will be assessed in multiple domains of functioning. We chose a family study approach as the main thrust of our research effort because of the highly developed sophistication of this methodology. It is expected that research data based on family studies can provide important information regarding the psychobiology of ADD. The sample for the proposed research includes a range of combinations of families. A total of 360 children and their families, chosen equally from a psychiatric (MGH) and non- psychiatric (HMO) settings, and within each setting, 60 each of ADD diagnosed children, 60 non-ADD children with some other psychiatric diagnosis, and 60 children with no-psychiatric diagnosis. The 180 children in the three HMO samples will be used to replicate results from the three MGH samples. The pilot studies have been completed and the data have been analyzed. The preliminary studies and significance sections describe the results in detail and explain how they support the proposed application. The aims of this proposal are to: 1. study the familial and psychosocial risk factors of ADD; 2. identify and test the validity of subgroups of ADD children based on the presence or absence of co-morbidity (i.e. conduct disorder, oppositional disorder, major affective disorder, anxiety disorder); 3. identify the clinical and familial predictors of course and outcome of these subgroups with co-morbidity; 4. evaluate the stability of the child's and parent's report of psychopathology after two years.